USA Baby Care's website makes no attempt to hide why the company's clients travel to Southern California from China and Taiwan. It's to give birth to an American baby.

"Congratulations! Arriving in the U.S. means you've already given your child a surefire ticket for winning the race," the site says in Chinese. "We guarantee that each baby can obtain a U.S. passport and related documents."

That passport is just the beginning of a journey that will lead some of the children back to the United States to take advantage of free public schools and low-interest student loans, as the website notes. The whole family may eventually get in on the act, since parents may be able to piggyback on the child's citizenship and apply for a green card when the child turns 21.

USA Baby Care is one of scores, possibly hundreds, of companies operating so-called maternity hotels tucked away in residential neighborhoods in the San Gabriel Valley, Orange County and other Southern California suburbs. Pregnant women from Chinese-speaking countries pay as much as $20,000 to stay in the facilities during the final months of pregnancy, then spend an additional month recuperating and awaiting the new baby's U.S. passport.

Many of the hotels operate in violation of zoning laws, their locations known mainly to neighbors who observe the expectant mothers' frequent comings and goings.

Such was the case in Chino Hills, where residents recently protested an alleged maternity hotel operating in a hilltop mansion. City officials have sued the property owner, claiming that the seven-bedroom house was illegally subdivided with 17 bedrooms and 17 bathrooms, with at least 10 mothers and babies living there. San Gabriel officials shut down a similar facility in 2011, and Chino Hills officials hope their lawsuit will result in a similar outcome.

Critics also cite safety concerns surrounding the largely unregulated industry. A local attorney says he is representing a maternity hotel in a case where a baby was dropped and died. The California Department of Public Health also is investigating a case that may involve maternity hotels, said a spokesman who said he could not provide further details.

Federal immigration authorities say no law prevents pregnant women from entering the country. The women typically travel on tourist visas and return home with their newborns, who will have the option of coming to the U.S. for schooling, sometimes while the parents remain in Asia. American citizenship is also considered a hedge against corruption and political instability in the children's home countries. For some, giving birth in the U.S. staves off hefty fines under China's one-child policy.

Maternity hotels have proliferated in the last decade as mainland China's new middle class tries to give its offspring every advantage. But birth tourism is not limited to Chinese and Taiwanese nationals. South Korean and Turkish mothers are also reported to pay thousands of dollars for package deals that include hotel rooms and assistance with the visa process.

Since the publicity surrounding the Chino Hills case, Los Angeles County officials have received at least two dozen complaints, mostly regarding sites in Rowland Heights and Hacienda Heights. Curt Hagman, a Republican assemblyman from Chino Hills, said he is looking into whether state government can play a role in addressing the issue.

Because of the increased scrutiny, some maternity tourism businesses are setting up shop in standard hotels, booking long-term stays for clients, according to Scott Wang, manager of China operations for USA Baby Care. Others are opting for apartment complexes, where zoning codes are more flexible and rents are cheap enough to serve a larger number of clients.

Until a few months ago, USA Baby Care was located on a Hacienda Heights cul-de-sac, in a large two-story house with a swimming pool. Now, it operates out of a hotel in Rowland Heights.

"We really want to make this industry legal," Wang said. "There's a demand for these birthing centers, so we should find a way to make them legal. Not a single one of us wants to operate by sneaking around."

The road to giving birth in the U.S. begins with an in-person interview at an American consulate in the woman's home country. Neither pregnancy nor the intent to give birth in the U.S. are disqualifying factors. The primary concern is making sure the applicant will not remain in the country indefinitely, the State Department said.

Likewise, U.S. Customs and Border Patrol officers do not refuse entry because a woman is coming to give birth.

"Obviously, the only reason it happens at all is because we permit it," said Mark Krikorian, executive director of the Center for Immigration Studies, which advocates reduced immigration. "They're not doing anything illegal. The question for policymakers is, 'Is this a good idea?'"